100 



iii Virginia early in May, and, from hearsay evidence, remain until "late 

 in the fall " or until " right cold weather." At the date of the present 

 writing, September 28, they are still as abundant as ever around Wash- 

 ington. The characteristic habit of clustering about the base of the 

 horn seems to exist only when the flies are quite abundant. When they 

 average only a hundred or so to a single animal, comparatively few will 

 be found on the horns. Moreover, as a general thing the horn-cluster- 

 ing habit seems to be more 

 predominant earlier in the 

 season than later, although 

 the flies may seem to be 

 nearly as numerous. The 

 clustering upon the horns, 

 although it has excited con- 

 siderable alarm, is not pro- 

 ductive of the slightest harm 

 to the animal. Careful study 

 of the insects in the field 

 show that they assume two 

 characteristic positions, one 

 while feeding and the other 

 while resting. It is the rest- 

 ing position in which they 

 are always found when upon 

 the horns. In this position 

 the wings are held nearly flat 

 down the back, overlapping 

 at base and diverging only moderately at tip (see Fig. 14). The beak 

 is held in a nearly horizontal position and the legs are not widely spread. 

 In the active sucking position, however, the wings are slightly elevated 

 and are held out from the body, not at right angles, but approaching 

 it, approximately an angle of 60 degrees from the abdomen. The legs 

 are spread cut widely, and the beak, inserted beneath the skin of the 

 animal, is held in nearly a perpendicular position, approaching that in 

 Fig. 13c. The fly, before inserting its beak, has worked its way through 

 the hairs close to the skin. While feeding, however, the hairs which 

 can be seen over its body do not seem to interfere with its speedy flight 

 when alarmed, for at a fling of the tail or an impatient turn of the head 

 the flies rise instantly in a cloud for a foot or two, returning again as 

 quickly and resuming their former positions. 



The horns are not the only resting places, for with the horns black 

 for 2 inches above their base we have seen the flies towards nightfall 

 settle in vast numbers upon the back between the head and fore 

 shoulders, where they can be reached by neither tail nor head. When 

 feeding they are found over the back and flanks and on the legs. Dur- 

 ing a rain-storm they flock beneath the belly. When the animal is 



Fig. 14. 



-Hematoma seerata: Adult in resting posi- 

 tion — enlarged. (Original.) 



